In order to conserve power, wireless mobile devices often enter a power save or sleep mode, where components of the mobile device consume little power (e.g., radio components are disabled or placed into a low power state) when there is no pending data for the mobile device to transmit or receive. For example, the 802.11 standard may be utilized to provide a power save feature for mobile devices, wherein a mobile device will periodically wake and listen for a beacon signal before returning to the power save mode. In this manner, the mobile device conserves power and prolongs the life of its battery.
Large wireless networks (such as wireless local area networks or WLANs), often utilize numerous access devices spread throughout an area, such as a warehouse, building or campus. In some situations, it may be desirable to determine the physical location of a mobile device on the wireless network. For example, a user may need to locate a mobile device that has been lost or misplaced. Alternatively, in some cases, a mobile device may be associated with some other object that a user would like to locate. For example, a mobile device may be mounted to a forklift, pallet, or another object that the user is trying to locate.
In some current wireless networks, it is possible to triangulate and determine the location of a mobile device. For example, if at least three access devices receive a frame from the mobile device at the same time, the physical location of the mobile device may be determined based on the physical location of the access devices and the respective signal strength of the frame at each access device. However, this method is difficult to effectively implement in practice because it relies on multiple access devices being able to receive the frame at the same time from the mobile device. For example, in most wireless networks, the access devices use non-overlapping channels, and thus only one access device typically receives the frame from the mobile device. Furthermore, once the mobile device enters into a power save mode or sleep mode, the mobile device no longer transmits frames on a regular basis. As a result, it is difficult to synchronize the access devices for receiving a frame from the mobile device, and as such, the prior art methods are ineffective without complex synchronization schemes and/or programming overhead.